Method of heating gear with highfrequency current



1947- w. M. ROBERDS 2,426,053

METHOD OF HEATING GEAR WITH HIGH FREQUENCY CURRENT Filed Feb. 27, 1945i7 Vlsle R0 2 3 2% (Ittomcg Patented Aug. 19, 194-? METHOD F HEATINGGEAR WITH HIGH- FB/EQUENCY CURRENT Wesley M. Roberds, Collingswood, N.3., assignor to Radio Corporation of America, a corporation of DelawareApplication February 27, 1943, Serial No. 477,473

(Cl. 2l9l3) 1 Claim. 1

This invention relates to the treatment of metals, and more particularlyto the heat treatment thereof for altering the hardness of the metal.

in many fields of use, it is desirable to harden the surface of metalsdue to the wear which they encounter. Various methods have been proposedheretofore for heating the metal. In connection with metals which areferrous in nature, it has been proposed to subject them to the influenceof an alternating magnetic field which induces eddy currents in thesurface and thereby effects heating thereof. In certain cases, it may bedesirable to avoid hardening of a particular portion of the metal, andthe primary object of my present invention is to provide a novel methodwhich will accomplish this.

More particularly, it is an object of my pres nt invention to provide animproved method of heat treating metals for altering the hardnessthereof whereby only predetermined or preselected parts thereof will behardened within a given or prescribed area.

Another object of my pre ent invention is to provide an improved methodas above set forth wherein the parts which it is desired not to hardenwill be very substantially protected from the heat source.

It is also an object of my present invention to provide an improvedmethod as above set forth which is economical to practice and highlyefficient in use.

In accordance with my invention, the parts of the metal article whichare to be protected and not heated are covered with a layer of a good,conducting material, such as silver or copper. This conducting layer,which may be eleotrodeposited on the article, applied thereto in theform of paint or the like, or simply held contact therewith bymechanical means, constitutes an electrical shield in the form of ashunt around the parts which are to be protected to thereby provide aprotective path which may or may not be of lower electrical impedancethan the portion or portions of the article which are to be protected.The protective coating should be disposed between the portion of thework to be protected and the induction coil by means of which themagnetic field is applied to the work. Thus, when the article issubjected to a very short exposure in an alternating magnetic field ofsufliciently high frequency (for example, at radio frequency), theconducting layer by-passes the induced eddy currents and preventsheating of the underlying material. In addition, since the coatingmaterials are usually good heat conductors, they also provide more rapidheat conduction away from the areas to be protected.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claim. The inventionitself, however, together with additional objects and advantagesthereof, will best be understood from the following description ofseveral ways in which it can be carried out in practice, when read inconnection with the accompanying drawing, in which Figure 1 is an endelevation of an article part of the surface of which is to be hardenedand the remaining surface of which is to be protected against hardeningin accordance with one form of the present invention,

Figure 2 is a sectional view taken on the line 11-11 of Figure 1,

Figure 3 is a view partly in elevation and partly in perspective of acylindrical article treated in accordance with a somewhat diiferent formof my invention,

Figure 4 is a sectional view taken on the line IVIV of Figure 3,

Figure 5 is a View similar to Figure 3 and showing a slightly differentway in which the present invention can be carried into effect,

Figure 6 is a sectional view taken on the line VIVI of Figure 5, and

Figure '7 is a plan view of a device for applying my present inventionspecifically to a spur gear.

Referring more particularly to the drawing,

wherein similar reference characters designate corresponding partsthroughout, there is shown, in Figures 1 and 2, a circular disk I offerrous material having a radial slot 3. Let it be assumed that it isdesired to harden all the circumferential surface of the disk 1 exceptthe portion thereof in the region of the corner A and the portion in theregion C at the bottom and lower sides of the slot 3. This may beaccomplished by first securing to the disk 1 adjacent the regions A andC a member 5 which has low electrical impedance as compared with themetal of the disk l. The member 5 may be a spring clip, for example,made of copper or the like and may simply be inserted into the slot 3 sothat the resilient loop but thereof, coacting with the sides of the slot3, will retain the member 5 in place. The member 5 should contact thedisk I at least at both its ends 5b and 50 whereby to provide a shuntpath around the regions A and C which has good electrically conductiveproperties.

teeth 9a.

The assembly may then be placed within a ring-like induction coil 1connected to a suitable high frequency oscillation generator through acurrent transformer (not shown) in a manner well know in the art. Thegenerator may be a vacuum tube oscillator operating at radio frequencyor at some suitable lower frequency which, like radio frequency, is highenough to effect heating of only a thin, skin or surface layer in thework, and the applicator or coil 1 is as closely spaced to the work asis practicable. The high frequency magnetic field set up by theinduction coil 1 induces eddy currents in the disk I near the surfacethereof to effect rapid heating of a skin surface layer la to atemperature sufhcient to harden the surface layer. However, in theregions A and C, very little heating will take place by reason of thefact that the eddy currents will be by-passed around these regionsthrough the relatively low impedance path 5. Thus, the heating isconfined substantially to the portion la and is very largely excludedfrom the regions A and C. As a result, only the region lc will becomehardened, while hardening of the regions A and C will be avoided. Afterapplication of the heat, the disk I is, of course, quenched in anysuitable manner, or it may be heated rapidly and self quenched asdescribed in the copending application of George H. Brown, Serial No.421,746, filed on December 5, 1941, and assigned to Radio Corporation ofAmerica.

In Figures 3 and 4, the conductive shunt is constituted by a strip 9 ofcopper, silver, or the like, placed over the area lid of a cylindricalmember H. The shunt 9 may be formed with serrations, scallops, or thelike to, whereby it contacts the surface of the cylinder H at onlyisolated points. The shunt 9 may be applied to the cylinder II in anysuitable manner, as by being clamped against it. When the assembly issubjected to an alternating magnetic field of radio or other suitablehigh frequency, the entire cylindrical surface of the cylinder H exceptthe region Ila thereof becomes heated by electromagnetic induction,since the shunt member 9 becomes the principal path for the eddycurrents which are thus shunted or bypassed around the region Ila. Theprotected area Ha of the cylinder does not particularly show a serratedlongitudinal region. represented by the serrations or In any case, it isapparent that the region I la will not become hardened, and only theremaining cylindrical surface of the cylinder II will remain hard afterquenching.

Instead of applying to the cylinder II a shunting strip such as thestrip 9, the area thereof to be protected may be covered with aconductive layer 13, as shown in Figures 5 and 6. For example, a layerof good, conductive paint may be painted on, sprayed on, or applied inany other suitable way, or a layer of good, conductive material may beelectrodeposited over the area of the cylinder which is to be protected.The ultimate result approximates the result obtained by an arrangementsuch as shown in Figures 3 and 4.

In Figure 7 there is shown an arrangement for protecting the tips of theteeth (5 of a spur gear IT. For this purpose, an insulated ring I!) maybe provided with a plurality of good electrically conductive, shuntingelements 2| corresponding in number to the number of teeth on the gear.Each of the elements 2| may be a spring clip which embraces and firmlyengages the outer regions of the teeth [5. When the assembly issubjected to the influence of an alternating magnetic field ofsufficiently high frequency, the eddy currents induced in the gear willheat the surface thereof, including all those portions of the teeth l5which are not embraced by the shunt ing elements 2!, but the regions I5athereof which are embraced by the shunting elements 2| will not besubstantially heated because the eddy currents will pass through themore highly conductive elements 21. If desired, the ring I9 may be madeof electrically conductive material to constitute the applicator orinductive coil coupled to the oscillator. In such case, it will benecessary to insulate each element 2| from the ring If; to avoidundesirable current paths.

Although I have shown and described several ways in which my presentinvention can be carried into effect, it will, no doubt, be apparent tothose skilled in the art, that the present invention is susceptible tovarious other modifications. Moreover, it should be apparent that thepresent invention may be used for hardening metals other than ferrousmetals, and that it may be used equally well for annealing metals suchas brass or the like wherein certain portions or areas are to beprotected from the annealing process, instead of for hardening.Wherever, in this specification and the appended claim, I have referredto heating of the entire article, or to heating all of the metal I donot necessarily intend to be limited to treatment of 100 per cent of thearticle or the metal, but only to that part thereof which is to behardened or annealed, as the case may be, and from which part thehardening or annealing of a portion or section is to be excluded. Withthe foregoing in mind, I desire that my invention shall not be limitedexcept insofar as may be necessitated by the prior art and by the spiritof the appended claim.

I claim as my invention:

In the method of manufacturing a gear composed of a material adapted tobe hardened by heating with alternating current of a sufficiently highfrequency to flow in substantially a thin layer at the surface thereof,the steps which comprise placing around the tip portions of the gearteeth conductive shields for the purpose of shuntin current around saidportions, and causing the high frequency heating current to flow throughthe remaining portions of said teeth and said shields.

WESLEY M. ROBERDS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Babat, Construction of HeatingCoils for Induction Surface Hardening, Heat Treating and Forging, April1941, page 192.

